1. Field of the Invention
This invention relates to a body structure of a motorcycle such as a scooter. More particularly, an overall frame of the motorcycle includes a front frame and a rear frame, which are respectively attached to a horizontally opposed engine and a transmission casing. By using the engine and transmission casing in the frame structure, there exists room for enlarging and lowering footboards along the bottom of the motorcycle's body structure.
2. Description of the Relevant Art
Generally, body structures of motorcycles are classified into ordinary body structures, and scooter type body structures. Japanese Patent No. 2593868 illustrates the ordinary body structure which characteristically includes a body frame wherein a front and rear portion of the body frame are directly coupled. An engine is suspended from the body frame using an engine hanger.
The scooter type body structure can be similar to the ordinary body structure, but with different shapes and details. One such scooter type body structure, as illustrated in Japanese Patent Publication No. Sho 37-16106, is a so-called monocoque body. In the monocoque, an engine and a swing arm supporting a rear wheel are attached to the body frame.
The ordinary body structure suffers drawbacks. If the front and rear portions of the frame are directly coupled, as in Japanese Patent No. 2593868, a joint between the front and rear frames or a rear end of the front frame is positioned at the center of the motorcycle, i.e., where footboards have to be provided. Therefore, the footboards will not have sufficient space because they are adversely affected by the front or rear frame. Further, the front or rear frames exist in a floor tunnel between the footboards, which the rider must step over when mounting or dismounting the motorcycle. The presence of the front or rear frames requires that the floor tunnel be made large in height, which makes it difficult for the rider to step over the tunnel area smoothly. This is not preferable in a scooter. A scooter should feature easy mounting and dismounting accomplished by use of the low footboards.
The monocoque body also suffers drawbacks. The monocoque body of Patent Publication No. Sho 37-16106 must be constructed by a special process. Components defining the profile of the motorcycle have to be produced by press-molding steel plates. Press-molded components must have complicated structures in order to maintain rigidity. Further, the number of components is increased, and complicated welding processes are necessary for the increased number of parts. This means that a manufacturing process becomes complicated and expensive, and the weight of the body is relatively heavier. In order to overcome the foregoing problem, a motorcycle usually includes a frame made of metallic pipes, which are joined and welded, and a body defining the profile of the motorcycle is made of molded resin.